1. Field of the Invention
This invention pertains to wells and more particular to gas wells. This invention is particularly directed toward a device for retrieving a pressure seal ball that has blown up or risen from the well to the casing head and jammed against the exit nipple thus trapping gas therebelow.
2. Description of the Prior Art
Gas wells are bored relatively deep in the ground; on the order of 4,000 to 8,000 feet. After a hole is sunk to gas bearing rock formations, a perforated casing is inserted to aid in permitting gas to exit therefrom without accompanying sand, broken rock or other debris. As the perforated casing is lowered into the hole, a series of horizontal plates are positioned in some of the casing joints, each plate having a round hole, axially or centrally located therein. The plates are stationed so that the smallest diameter plate hole is located at or near the bottom of the well hole and are progressively larger in diameter as they near the surface of the earth. The largest hole is approximately 4 inches in diameter which is the nominal diameter of the casing itself.
It is necessary that the rock formation through which the well passes be fractured to create a labyrinth of fracture lines or cracks from which the trapped natural gas may escape into the well casing. This is accomplished by either detonating explosive charges within the well casing or by filling the casing with hydraulic fluid and exposing the fluid to extreme pressure.
In both instances, it is desirable to stratify the area of extreme pressure to maximize the effectiveness of the fracturing operation. This is accomplished by dropping spherical composition or plastic balls of desired diameter into the well so that they lodge in the holes of the plates and shut off fracturing operations from below; hence the term "pressure seal" balls, as they seal the fracturing operations from lower areas of the well.
After the desired subterranean sections of the well are fractured, the top of the well casing, or wellhead, is closed off and gas flow from the fractured area is permitted into the well casing until the gas pressure has reached a steady state condition, normally within the range of 2,000 to 2,500 lbs. pressure. The wellhead is thereafter quickly opened to vent the trapped gas; the high pressure discharging gas blows debris, and, hopefully, the pressure-seal balls out of the casing.
After the well is "blown," the wellhead or upper part of the well casing is connected to commercial gas transportation lines. For cost considerations, the 4-inch casing exiting the ground is reduced to 2 inches nominal diameter by use of a reducing nipple and a 2-inch ball or gate valve is attached thereto to control gas flow to the commercial transportation lines. The reason for this is that a 4-inch ball or gate valve costs upwards of $1,200.00 whereas a 2-inch diameter ball or gate valve costs only $400.00 and is far easier to actuate.
A commonl problem in the industry has been the occlusion or entrapment of a pressure-seal ball below one of the plates during gas well blowing. The ball does not dislodge during blowing and float upwards to the wellhead valve sometime after the well has been put into service on a commercial gas line. The ball than becomes trapped in the reducing nipple below the 2-inch wellhead valve and gas pressure in the well increases to 2,000 to 2,500 lbs. pressure. Removing the wellhead 2-inch valve will result in a tremendous explosion of high pressure gas, loss of gas, possible fire and possible personal injury from flying debris or the trapped ball. Without removal, the jammed ball effectively shuts off the well below the 2-inch valve.
The use of a 4-inch ball or gate valve below the 2-inch wellhead valve provides an effective means of shutting off the well to allow removal of the nipple and removal of the ball; however, this results in a continuing necessity to keep a 4-inch, $1,200.00, valve on every wellhead in addition to the 2-inch, $400.00, wellhead control valve. To date, no one has been able to effectively devise a method and/or apparatus to remove a stuck pressure-seal ball from the wellhead without the use of the very expensive dual valve system.